At 1k tabs firefox was snappy and responsive, but at 5k tabs it was bad, very unstable, buggy and sluggish.
Firefox would crash often even doing simple tasks, some times it took 2 or 3 tries to open firefox. scrolling through all the tabs a couple of minutes.
But all good things must come to an end. Now I close any extra tabs, have 5 - 30 tabs open.
Something like that.
At first I opened tabs for ”This sounds interesting I will read / watch it later” or ”I'll probably need it later” This got me to ~300 - 800 tabs but then it became a joke, I just left tabs open knowing full well where not needed.
Some times keeping all tabs open payed off like, using the search feature to find back to a project I left off. This happened very rarely.